The invention relates to a method for modifying the irradiance distribution of a radiation source according to the preamble of claim 1.
The invention also relates to a device for modifying the irradiance distribution of a radiation source.
Especially one of the preferred embodiments of the invention relates to evening the irradiance distribution of a radiation source on a large planar target surface.
In many applications, especially in photographic exposure and heating applications, the uniform illumination of a large plane is a highly desirable and even a necessary feature. For example, the irradiation intensity from an isotropic point source falling on a planar surface follows the formula
I=I0cos3(xcex8)xe2x80x83xe2x80x83(1)
where xcex8 is the angle of incidence of the illumination with the plane and I0 irradiance on the symmetry axis of the circular illumination pattern while, to achieve a deviation of intensity of less than xc2x15% over a 1.6-m diameter plane area, the point source must placed at a distance of 4.3 m. The corresponding formula for a Lambertian surface light source is
I=I0cos4(xcex8)xe2x80x83xe2x80x83(2)
the distance for the same intensity deviation being 5.0 m. In practice, the lamp itself can be approximated with the point-source formula and the lamp reflector with the Lambertian surface light-source formula.
Traditionally, uniform illumination has been created, e.g., by means of an array of light sources, using a carefully designed reflector behind the light source (e.g. U.S. Pat. Nos. 3,763,348 and 4,027,151), by means of a carefully designed lens system between the light source and the plane (e.g. U.S. Pat. No. 5,555,190), and also by scanning the plane with the light source.
In many applications, the use of an array of light sources incorporating plane-to-plane illumination systems is too cumbersome, expensive, and power consuming. The main shortcoming of even very carefully designed back reflectors is that the illumination distribution created is very sensitive to the dimensions of the light source and reflector and especially to the position of the light source in relation to the reflector. This also applies to the use of carefully designed lens systems, such lens systems being, in addition, far too expensive in many applications. The scanning method is suitable only for a limited number of applications and a complex mechanism is required to perform the scanning operation.
The present invention is intended to overcome the drawbacks of the techniques described above and to achieve an entirely novel type of method and device for modifying the power distribution of a radiation source.
The invention""s goal is achieved by using a combination of non-absorbing and/or absorbing plates to attenuate the irradiation of areas close to the optical axis by reflecting back and/or absorbing the incident radiation in that region and, additionally, to use an optional diffuser plate to diffuse incident light from the light source and to redirect light reflected back from the plate stack onto the diffuser into a wider angular distribution
More specifically, the method according to the invention is characterized by what is stated in the characterizing part of claim 1 and the device by what is stated in the characterizing part of claim 6.
The invention offers significant benefits.
Compared to the prior art, the invention permits a substantial reduction in the distance between the light source and the plane to be illuminated. This feature particularly permits smaller solar panel testing devices, bringing considerable savings in space utilization. Especially when mainly transparent elements are used to equalize the light pattern, losses of light energy are minimal. In addition, the shorter distance between the light source and the target area allows the use of light sources of lower energy.